Instrument Landing System

Instrument Landing System仪表着陆系统An instrument landing system(ILS) is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow.Instrument approach procedure charts (or approach plates) are published for each ILS approach, providing pilots with the needed information to fly an ILS approach during instrument flight rules (IFR) operations, including the radio frequencies used by the ILS components or navaids and the minimum visibility requirements prescribed for the specific approach.Radio-navigation aids must keep a certain degree of accuracy (set by international standards of CAST/ICAO); to assure this is the case, flight inspection organizations periodically check critical parameters with properly equipped aircraft to calibrate and certify ILS precision.仪表着陆系统是为飞机进近和在跑道上着陆提供精密导航的一种地面基站仪表进近系统，它将多种无线电信号结合使用，在许多情况下，高度密集的灯光阵为飞机提供一个仪表飞行气象条件（比如说低云层或者由于雾、降雨或者暴风雪引起的低能见度条件）下的安全着陆条件。

仪表进近程序航线图（或者进近平面）为每一次的仪表着陆进近中的飞行员在仪表飞行准则操作（包括仪表着陆系统部件或者助航装置使用的射频以及特殊进近要求的最低能见度）中提供必要的信息来进行仪表着陆进近。

无线电导航协助必须保持某一个精度（这个精度是国际民航组织制定的）；为了确定这一点，飞行检查组织必须定期地检查拥有良好配置的飞机的临界参数以校准和确定仪表着陆系统的精度。

Principle of operationAn ILS consists of two independent sub-systems, one providing lateral guidance (localizer), the other vertical guidance (glide slope or glide path) to aircraft approaching a runway. Aircraft guidance is provided by the ILS receivers in the aircraft by performing a modulation depth comparison.A localizer (LOC, or LLZ until ICAO designated LOC as the official acronym) antenna array is normally located beyond the departure end of the runway andgenerally consists of several pairs of directional antennas. Two signals are transmitted on one out of 40 ILS channels in the carrier frequency range between 108.10 MHz and 111.95 MHz. One is modulated at 90 Hz, the other at 150 Hz and these are transmitted from separate but co-located antennas. Each antenna transmits a narrow beam, one slightly to the left of the runway centerline, the other to the right.操作准则：仪表着陆系统由两个独立的子系统组成，其中一个提供水平方向的导航（航向信标），另一个提供垂直方向的导航（下滑信标），这两个信标为飞机提供跑道进近。

飞机导航是由飞机上面的仪表着陆系统接收机通过比较调频深度来提供的。

航向信标的天线阵一般是在跑到尽头的分支点，它是由数对定向天线组成的。

两个信号是由基于108.10MHz到111.95MHz载波频段的40个ILS频道中的一个发出的。

一个信号调频到90Hz，另一个调频到150Hz，这些是由分开但是协同工作的天线发出的。

每个天线发送一个窄波，一个在跑道中心线左边，另一个在跑到中心线右边。

The localizer receiver on the aircraft measures the difference in the depth of modulation (DDM) of the 90 Hz and 150 Hz signals. For the localizer, the depth of modulation for each of the modulating frequencies is 20 percent. The difference between the two signals varies depending on the position of the approaching aircraft from the centerline.If there is a predominance of either 90 Hz or 150 Hz modulation, the aircraft is off the centerline. In the cockpit, the needle on the horizontal situation indicator (HSI, the instrument part of the ILS), or course deviation indicator (CDI), will show that the aircraft needs to fly left or right to correct the error to fly down the center of the runway. If the DDM is zero, the aircraft is on the centerline of the localizer coinciding with the physical runway centerline.飞机上面的航向信标接收机测量出90Hz和150Hz信号的调频深度的不同。

对于航向信标来说，每次调频的调频深度为20%。

信号不同的情况是取决于飞机进近时相对于跑到中心线的位置。

如果90Hz信号和150Hz信号调频中有一个信号更强，那么飞机就偏离了跑到中心线。

在驾驶舱里面，水平状态指示器或者偏航指示器上面的指针（HIS，ILS的仪表部分）将会指示出飞机需要向左或者向右飞行来修正错误以对准跑到中心线。

如果调频深度差值为零，那么飞机就对准了位于跑到中心线上面的航向信标。

A glide slope (GS) or glide path (GP) antenna array is sited to one side of the runway touchdown zone. The GP signal is transmitted on a carrier frequency between 328.6 and 335.4 MHz using a technique similar to that of the localizer. The centerline of the glide slope signal is arranged to define a glide slope ofapproximately 3° above horizontal (ground level). The beam is 1.4° deep; 0.7° below the glideslope centerline and 0.7° above the glideslope centerline.These signals are displayed on an indicator in the instrument panel. This instrument is generally called the omni-bearing indicator or nav indicator. The pilot controls the aircraft so that the indications on the instrument (i.e., the course deviation indicator) remain centered on the display. This ensures the aircraft is following the ILS centreline (i.e., it provides lateral guidance). Vertical guidance, shown on the instrument by the glideslope indicator, aids the pilot in reaching the runway at the proper touchdown point. Many aircraft possess the ability to route signals into the autopilot, allowing the approach to be flown automatically by the autopilot.下滑信标位于跑到触地区域的一端。